nbc news is able to report tonight that dzhokhar tsarnaev has told investigators he and his brother acted alone, they learned to build pressure cooker bombs over the internet, and were motivated by a desire to defend islam because of the wars in iraq and afghanistan. now, that early reporting may prove to be wrong. it may prove that the suspect retracts those statements later or maybe he's lying or he might be confused. but there is a small but significant cornerstone to build from that was not there before. we have left the realm of pure, complete speculation inside which would be frankly irresponsible to address questions of motives in the first place. in the case of dzhokhar tsarnaev even as we learn more about him and his life leading up to the bombing and what he is telling investigators, the question of why is intensely mysterious. if you spend some time on his twitter page as i did on the day it was first reported that he was a suspect, you'll find a teenager who mostly seems interested in stuff like weed, hip hop, girls, cars. it does not read like the twitter feed of someone who